1. Field of the Invention
The invention relates to a method for the production of a disk-shaped silicon semiconductor component with at least two adjoining zones of opposite type conductivity and different doping strengths where the bounding surface of the semiconductor disk opposite the plane of the pn-junction separating the two zones is beveled with a rotating lapping disk at a shallow angle oriented so that the cross section of the semiconductor disk is smaller on the highly doped side than on the side with lower doping (negative beveling).
2. Description of the Prior Art
In a known method the beveled surface is produced in a grinding or lapping process using a steel block in the upper surface of which is provided a spherical depression, the radius of curvature of which corresponds to a first bevel angle to be generated (DE-PS 1 212 215). A grinding paste is distributed over the surface of the depression. The silicon disk is laid in the depression, the circumference of one of the main surfaces of the disk then being in contact with the surface of the depression.
In the known case the silicon disk is rotated, but of course the relative rotary motion can also be produced by rotation of the grinding or lapping disk. To produce a very shallow angle, several steel blocks with spherical depressions of increasing radii of curvature must be used in succession. This method consequently requires costly equipment.
The aim of the negative beveling is to lower the maximum field strengths at the surface of the semiconductor component. In DE-AS 1 281 584 an optimal negative angle of 6.degree. is mentioned. It is known, however, that for reduction of the surface field strengths still shallower angles are desirable (IEEE Transactions on Electron Devices vol. ED-20, no. 4, April 1973, pp. 347-352). In this reference it is further shown that the absolute field-strength maximum actually develops somewhat below the bounding surface of the silicon disk and that rather small bevel angles always cause reduction in the maximum field strength, and indeed the more so, the flatter the doping profile and the higher the n-base doping. It is assumed here that an n-doped silicon disk is involved.
The realization of a very shallow bevel is limited to the extent that the effective current-carrying cross section is decreased by it. For circumventing this problem it is known how, by an alternation of diffusion and mechanical etching processes, to create in the edge region of the silicon disk a pn-junction extending at least approximately along an obtuse conical surface, the bounding surface of the silicon semiconductor disk likewise being made obtusely conical (DE-OS No. 1 904 798). Such an alternation of different fabrication steps can be undesirable from the technical viewpoint of manufacture.
The starting point here, therefore, is the initially discussed known method for the production of a disk-shaped semiconductor component, in which the beveling is done only in the region of the pn-junction emerging at the bounding surface.